1. Field of the Invention
The present invention relates to a buffer data control circuit and method. More particularly, the present invention relates to a circuit and method which controls the amount of image compression data, which is processed in an image compression system using wavelet transform, accumulated in a channel buffer.
2. Background Art
In general, image compression is performed for the purpose of reducing the bit rate of input image data for its transmission, or improving the efficiency of a storage for storing the image data. A conventional image compression system using a discrete wavelet transform is shown in FIG. 1. Referring to FIG. 1, a discrete wavelet transformer 10 wavelet-transforms an input digital image applied thereto, and outputs a wavelet signal having a configuration which is shown in FIG. 3. A vector assembly 20 receives the wavelet signal, and generates a wavelet signal having a DC coefficient and wavelet signal having an AC coefficient.
A differential pulse code modulator 30 differential-pulse-code-modulates the wavelet signal having a DC coefficient, to convert it into a differential wavelet signal, and supplies this differential wavelet signal to a scalar quantizer 40. Scalar quantizer 40 scalar-quantizes the differential wavelet signal, and supplies it to a Huffman encoder 50. Huffman encoder 50 encodes the scalar-quantized differential wavelet signal, converts it into a DC compression signal, and supplies the DC compression signal to one input terminal of a multiplexer 80.
A vector quantizer 60 receives the wavelet signal having an AC coefficient from vector assembly 20, vector-quantizes it, and supplies the vector-quantized wavelet signal to another Huffman encoder 70. Huffman encoder 70 encodes the vector-quantized wavelet signal having AC coefficient, converts it into an AC compression signal, and supplies this AC compression signal to the other input terminal of multiplexer 80. Multiplexer 80 transmits the AC compression signal and DC compression signal to a network through a channel, according to a selection signal supplied by a system controller (not shown).
When a 30 frames/sec color image in quadrature common intermediate format is compressed at 55:1 in the above-described image compression system using wavelet transform, the number of bit transmitted through the channel for one second equals 30.differential.e 188.differential.e 144.differential.e8.differential.e2.differential.e2.differential.e (1/55).apprxeq.472,529.4 bits/sec. When motion estimation is added to the compression system in the direction of reducing the temporal redundancy of a motion picture, using full search algorithm, to obtain five-fold compression effect, the number of bits transmitted per one second becomes 94,505.9 bits/sec. However, this value, 94,505.9 bits/sec, is relatively large when compared to the channel capacity of 28.8 kbits/sec currently available for transmitting data through the public switched telephone network (PSTN) by means of a modem. Accordingly, in order to transmit image data of this bit rate through a modem, it is required that either the number of transmission frames per second be reduced, or the source data of the digital image be compressed at higher compression factor which invariably results in a deterioration in the picture quality.